Well-established power distribution systems exist throughout most of the United States, and other countries, which provide power to customers via power lines. With some modification, the infrastructure of the existing power distribution systems can be used to provide data communication in addition to power delivery, thereby forming a power line communication system (PLCS). In other words, existing power lines that already have been run to many homes and offices can be used to carry data signals to and from the homes and offices. These data signals are communicated on and off the power lines at various points in the power line communication system, such as, for example, near homes, offices, Internet service providers, and the like.
Power distribution systems include numerous sections, which transmit power at different voltages. The transition from one section to another typically is accomplished with a transformer. The sections of the power distribution system that are connected to the customers premises typically are low voltage (LV) sections having a voltage between 100 volts(V) and 1,000V, depending on the system. In the United States, the LV section typically is about 120V. The sections of the power distribution system that provide the power to the LV sections are referred to as the medium voltage (MV) sections. The voltage of the MV section is in the range of 1,000V to 100,000V. Overhead MV power line conductors, which are typically not insulated conductors, are typically insulated from utility poles and other support infrastructure by electrical insulators. The transition from the MV section to the LV section of the power distribution system typically is accomplished with a distribution transformer, which converts the higher voltage of the MV section to the lower voltage of the LV section. PLCSs may communicate over both the MV and LV power lines.
A common problem encountered during data communication in PLCSs is noise generated by the various components of the electrical distribution system. Ingress noise may also be coupled into the PLCS system from the general RF (radio frequency) environment as the power lines themselves act as antennas. It is therefore convenient to categorize the observed noise into two components, the first of which has a strong 60 or 120 Hz periodicity (“buzz” noise) and a second in which the 60 or 120 Hz periodicity is weak or entirely absent (“hiss” noise). Buzz noise is generally due to micro-sparks, corona discharge or partial discharge mechanisms in insulators as a result of the voltage potentials applied by the electric utility. This noise tends to be localized to the source. Hiss noise, as mentioned previously, is related to RF ingress and tends vary much more slowly with distance across larger geographic areas.
Additionally, buzz noise may be predictive of failure of one or more parts of the electric utility network. For example, for overhead power lines such as medium voltage power lines, insulator failure may be result from wear, weather factors, vegetation contact and other causes. One method for locating noisy insulators involves physical surveys, but such surveys are difficult and frequently non-productive since fully quantitative noise measurements are almost impossible with simple, portable equipment that can be operated by utility line personnel. No quantitative and systematic method exists today that allows large areas of the electric utility infrastructure to be monitored for RF noise.
Therefore, there is a need for a systematic, quantitative method of determining information regarding both the type and the location of power line noise sources so that the operator of the system can take appropriate action.